Astronomy 101 Planetarium Lab

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## Astronomy 101 Planetarium Lab

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**Astronomy 101 Planetarium Lab**Instructor: Brian Pohl ConOps: Craig Zdanowicz www.physics.unc.edu/~bpohl/ PLEASE SIT IN SAME SEAT AS LAST TIME!!**Morehead Observatory Guest Night**Each Friday night that UNC classes are in session. Reservations, email Sallie Anderson sallie@physics.unc.edu**Celestial Navigation**• Is the Earth round or flat? • How can we measure the size of the Earth • How can we determine where on the Earth we are? Where in the World Are We??**STARS!!**• The Celestial Sphere • The position of stars is “constant” • The CS is “stationary” relative to the Earth • We need to measure angles • Need a method more precise than hand measurements. • But first we measure the Sun!**Earth’s Circumference and Diameter**7.2° 5000stadia ―― = ―――――― 360° circumference Eratosthenes (~ 225 B.C.E.)**Lines of Latitude are parallel, and resemble**the coordinate of Declination on the Celestial Sphere. Lines of Longitude converge at both poles, Meaning they are NOT parallel. This coordinate Is analogous to the coordinate of Right Ascension.**Measure Radius of Earth**• We observe Arcturus (arc-to-Arcturus) from Chapel Hill and from Key West • Measure the angle from Arcturus to zenith at each location • Remember to use the calibration ratio • Note the mileage (BOOK IS WRONG) • New starting mileage: 11,666! • Angular difference is arc of Earth • We know angle (convert to radians) • We know miles between two • Calculate radius of Earth • As always, calculate %error for all measurements! LST 14h13m**Measure Latitude**• Move to South side of Planetarium • The Planetarium is least like the sky at horizon so we wish to minimize the distortion by moving South • DO NOT USE CALIBRATION RATIO!! • Polaris is stationary in sky, no clocks required • Latitude is the angle bet. Polaris and Horizon • Measure Latitude for Chapel Hill • As always, compute percent error**Measure Longitude**• This is our version of a good clock • We will perform the same measurement at different longitudes (Chapel Hill, Memphis) at the SAME TIME!! • Measure Spica to Meridian • ‘Spike to Spica’ • Calculate the angular difference • SIGN IS VERY, VERY IMPORTANT!!! LST 13h25m**Memphis Longitude**• DO NOT CALCULATE DISTANCE TO MEMPHIS!! • We want to know the longitude of Memphis • This is different from the book! • Note direction of angle (+ or -) • Chapel Hill Longitude = (-79degrees) • Memphis Longitude = CHlong – Ang. diff. • Does your answer make sense? • Is Memphis East or West of Chapel Hill? • What does the ‘-’ mean in the CH Longitude? • Calculate percent error, of course!!**The Lab Report**• Rewrite ALL the data • Include sample calculations • Staple the original data sheet to end of lab • Three measurements, three percent errors! • Radius of Earth • Chapel Hill Latitude • Memphis Longitude • Two sources of error**All Power Points are on my**website:http://www.physics.unc.edu/~bpohl Visit office hours or email me if you have questions! bpohl@physics.unc.edu NEW OFFICE HOURS Morehead room 403 Mondays, Tuesdays (week-after-lab) 3:00pm-5:00pm